At one point in The Cutting Room, Louise Welsh describes a bison's head, steeped in arsenic and mounted in a Glasgow saloon bar. The trophy is a century old but, because preserved in poison, still a dangerous presence. That's exactly what Welsh has done with an ossified, leathery old genre: marinaded it in a heady brew of her own.

Her hero, Rilke, is a house clearance expert, pleased as Aladdin at the treasure trove he finds in a house owned by the ancient Miss McKindless, who is on her last legs. She wants him to dispose of her dead brother's accumulated belongings, and Rilke thinks he's found the good stuff that every auctioneer hankers after: the hoary collectibles and antique evidence of gracious living. Hidden in the old devil's study, though, is the real stuff - the rare dirty books from Olympia Press and the filthy eight-by-tens slipped inside a buff envelope. These photos depict the sexual torture and murder of a young woman some time in the past. The photos are in black and white, and the glimpses of soft furnishings suggest Paris.

Glasgow is a place awash with its own perverse delights, however, and Rilke is our guide through its hidden backrooms as he turns detective. The girl in the pictures has perplexed and frightened him. His ramshackle investigations into her decades-old murder is an attempt to make amends; Rilke feels implicated somehow in the world that exploited and wasted the girl.

The amateur detective, the cruising flaneur, the queer auctioneer and his dubious friends: it's the kind of set-up that makes the reader anticipate further adventures for Rilke and co; his crew of rough trannies, bent coppers and Merlot-slugging femmes fatales. Like any genre plot it makes us want more, and its world is strangely cosy. We know we're confined by the safe walls of certain conventions.

Welsh self-consciously uses these conventions to draw us in. She understands that every fictional detective is a fetishist. They don't really want to find all the answers: the body in question, the confrontation with actual flesh. At that point their story would be over. Genre always wants to kill character, to grind it up in the merciless, mechanical drive towards resolution. Any detective protagonists worth their salt know this and try to involve us, en route, in the fabric of their lives. We get curious detours, red herrings, casual shags. Like the best genre heroes, Rilke has very idiosyncratic adventures. He's on a desperate sniffing trail, sorting through shucked-off evidence in a city and a book that seem to be teeming with fetishists of all kinds. While Rilke sorts out and packs up the house of the dead, his enemies and allies are trannies comparing manicures and chignons, bibliophiles who hoard musty paper, pornographers who hide their true business behind layers of obfuscation.

This is what Welsh is very good at. We get a lovingly detailed and grimy catalogue of impedimenta. The book is full of stuff: erotic ivory netsukes hidden in jacket pockets; worn stone steps in tenement buildings; shirts with armpit stains like weak tea. It is this kind of concreteness and eye for detail that makes The Cutting Room a literary novel - pulling us closer to life than most generic efforts.

It's less successful when it gets self-consciously literary and chimes off Girodias or Foucault, or presents its tombstone chapter epigraphs to lend some clout. The book doesn't need these kind of paperweights. There's a lovely weightiness here already; the real, immediate flesh, tantalisingly apparent under the make-up of convention. We see a transvestite being filmed in a bar, grinning and displaying receded gums and nicotine-stained teeth. Every disguise is cracked open and, as Rilke surveys it, his reactions are alternately steely and compassionate. He's a fascinating lead, taking us round every bolt-hole in the plot, where each character is seething with their own preoccupations, corrupted by their connections, and pushing us further into a mystery that winds up being all about the white slave trade.

But we really don't mind much about that. The final revelations come a bit quickly and don't quite live up to the rest of the book: that's another convention we're used to. Our real business as readers lies elsewhere, in the hoarding of clues, glimpses, and that delicious sense of things happening just around the corner. The fun lies in "trying to reach past the two dimensions of the image", just outside the frame, as Rilke tells us; but we know that once we get there, it's all over. When we actually find out who was dead and who wasn't and who was killed in the first place, we feel a bit deflated. We want more mysteries, more dropped evidence; more tease, less strip.

This gleefully black, knowing first novel - longlisted this week for the Guardian first book award - mostly delivers just that. Death and love all mixed up, and with love coming out on top.